Both angiotensin II and the prostaglandins, PGE2 and PGA2, can be formed within the kidney. It is therefore reasonable to assume that these substances may have important physiologic roles within the kidney. Utilizing the micropuncture technique, we plan to define the physiologic influence of angiotensin II on the resistance in the afferent and efferent arteriole of the superficial cortical nephron and upon sodium reabsorption in the superficial proximal and distal convoluted tubules of the rat kidney. Secondly, we propose to determine the direct influence of the prostaglandin, PGE2 and PGA2, on sodium reabsorption in the superficial proximal and distal convoluted tubule of the rat kidney. It has been suggested that changes in the perfusion pressure to the kidney may be an important regulator of renal sodium excretion. Utilizing an isolated kidney preparation and micropuncture techniques, we propose to define the influence of changes in perfusion pressure on sodium reabsorption in the proximal and distal convoluted tubules and in the loop for Henle of the superficial rat nephron. Furthermore, we propose to characterize changes in net Starling forces across the paritubular capillary as the perfusion pressure is varied. Hypertensive man is known to respond to an infusion of sodium with a natriuresis which is more prompt and pronounced than that observed in normotensive man. Utilizing micropuncture techniques, we propose to define the locus and nature of this response within the kidney. For this study, spontaneously hypertensive rats (SHR) will be used. It is felt that these rats are a reasonable model of human essential hypertension.